Student 01: The write up for atomic oxygen is good, but a few of the directions could have been fulfilled
more directly. For instance, the directions explicitly ask for DOI numbers. Also, the article which you are
evaluating is not identified. Which of the three gave your summary as its material? The third article is
missing the link or the upload.
Student 02: Very good find. The MISSE experiment was a good step in trying to get environmental
effects on materials under wraps. Another good mission was LDEF in the shuttle era.
Student 03: Very good find. I knew that the Hubble mission was one which presented higher than
expected thermal effects due to accelerated degradation of the thermal protection system. I remember
something about the thermal blankets being “grey” instead of their natural white color. This is an
excellent find of on-orbit data. And, professors are always suckers for pictures.
Student 04: PICTURES! All professors love pictures. In this case MISSE and LDEF make for some pretty
ones (and drastic as well). The high loss rates for the experiments shows how parts of your spacecraft
may simply waste away if not designed properly. This becomes particularly difficult when you wish to
run a mission for 5, 7, or 10 years. Good find. And I like the upload as well. I am a fan of Hubble for lots
of reasons, including how much we learned from the servicing missions.
Student 05: 38 hours is not a long time in terms of space environment exposure; however, it seems that
the experiment designers got something out of it. Maybe the lesson is that even a little amount of time
can start the process on its way. One interesting point is that some very interesting reactions happened
in the short duration that have long lasting effects with relation to further erosion.
Student 06: The data is wonderful and an excellent example of solar impact on space assets. However,
the assignment specifically asked for atomic oxygen degradation.
Student 07: Good find. I particularly liked the tie in with LDEF.
My articles:
(Peters, Gregory et al. 1986)
(Reddy 1995)
(Tonon, Duvignacq et al. 2001)
Peters, P. N., et al. (1986). "Effects on optical systems from interactions with oxygen atoms in low earth
orbits." Appl. Opt. 25(8): 1290-1298.
Modifications of material surface properties due to interactions with ambient atomic oxygen
have been observed on surfaces facing the orbital direction in low earth orbits. Some effects are
very damaging to surface optical properties while some are more subtle and even beneficial.
Most combustible materials are heavily etched, and some coatings, such as silver and osmium,
are seriously degraded or removed as volatile oxides. The growth of oxide films on metals and
semiconductors considered stable in dry air was measured. Material removal, surface
roughness, reflectance, and optical densities are reported. Effects of temperature,
contamination, and overcoatings are noted.
Reddy, M. R. (1995). "Effect of low earth orbit atomic oxygen on spacecraft materials." Journal of
Materials Science 30(2): 281-307.
Tonon, C., et al. (2001). "Degradation of the optical properties of ZnO-based thermal control coatings in
simulated space environment." Journal of Physics D: Applied Physics 34(1): 124.
Optical absorption and photoluminescence spectroscopy have been used to investigate the
physical changes induced by proton and electron irradiation in selected thermal control
coatings. This study focused on a white paint and on its two components, a
polydimethylsiloxane resin and zinc oxide powder. Samples were irradiated by either 45 keV
protons (fluence up to 10 16 protons cm -2 ) or 400 keV electrons (fluence up to 6×10
15 electrons cm -2 ). In situ reflectance measurements were made during the test and were
complemented after air introduction by photoluminescence characterization. The optical
properties of the paint are essentially those of the ZnO pigment. The optical degradation of the
material appears to be correlated with the density of defects created by ionization in a zone
close to the surface of the paint and called the optical thickness of the material. Two
degradation regions of the reflectance properties in the wavelength range 250-2500 nm have
been identified: one in the infrared and one in the visible blue region. The degradation in the IR
region disappears on exposure to air so that no complementary technique could be used for
identifying its origin. The point defects responsible for the optical degradation of the paint in the
blue region are singly ionized oxygen vacancies (F + centres) either initially present in the
material or induced by irradiation. Irradiation quenches the green photoluminescence emission.
The latter would be excited by the recombination of doubly ionized oxygen vacancies with
photoformed electrons of the conduction band.
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